The invention relates to a mechanical device designed to dissipate kinetic energy, such as (part of) the kinetic energy of a vehicle seat (in particular an aircraft passenger seat) and its occupant, when involved in a survivable accident or incident (such as an emergency landing of an aircraft).
More particularly the invention relates to such a device which can be used in connection with vehicle seats provided with shoulder belts.
The expression “vehicle seat” as used in the present text refers to seats that are appropriate for road or other surface transport vehicles and for air transport vehicles; the vehicle seats to which the invention most suitably applies are seats for public transport vehicles and aircrafts.
Several energy absorbing systems for transport category aircraft seats have been proposed in the art.
Most of the know systems are however designed to absorb the energy in the underframe structure of the seat. Reference can for instance be made in this respect to the following patent publications: DE 440 57 53, GB 2243540, U.S. Pat. No. 5,699,984, U.S. Pat. No. 5,069,505, U.S. Pat. No. 4,861,103.
These known systems present serious drawbacks in view of the new standards for seats in transport category aircrafts issued in June 1998 by the U.S. Federal Aviation Administration (FAA) and the European Joint Aviation Authorities (JAA), to improve the chances of passenger survival in emergency landing. Essentially the new rules are contained in the FAR/JAR 25-561/562. Of utmost importance to the background of this Patent, is the section prescribing:    1. In § A and § B, the emergency landing conditions governing the design of the seat and restraint system supposed to protect the passengers.    2. In § C, a set of performance pass/fail criteria, related to the human body tolerance to impact loads, that must not be exceeded during the dynamic tests conducted in accordance with § A and § B of this section, in particular the Head Injury Criteria (HIC).
The above set of criteria for seats design is well known by the air transport industry and aircrafts & seats manufacturers since June 1986. It appears however that the new performance standards prescribed in § C didn't receive appropriate attention.
Most of the redesign effort was focused on the seat structure to comply with the § A and § B, leaving the protection of the occupants to a patchwork of partial measures for most of the requirements of § C, resulting in no solution regarding the HIC, with however the exception of an inflatable lap belt system, derived from the air-bag technology, associated to a conventional seat structure.
According to the new rules, the former impact load required to be sustained by the seat structure, and its tie-down to the floor, was raised from a 9 g static load to a dynamic impact pulse triangularly shaped, peaking at 16 g. To meet that condition, most seat manufacturers developed various means to absorb part of the kinetic energy involved, in order to smooth off the peak of the 16 g pulse at a level acceptable by both the structure of the seat and its tie-down to the floor.
This process has however its limitations:    Because the space available between seat rows is limited, to protect the egress path of the passengers in emergency conditions, the maximum stroke allowed to the seat structure by any type of energy absorption device is limited to 3 inches by the airworthiness authorities.    While this stroke might provide some smoothing off the peak dynamic pulse, it has practically no effect on the occupant excursion. Instead he will be allowed to pick-up speed relatively to the seat or the bulkhead in front, resulting in a secondary impact of the head which can be lethal.
In view of this, one approach to meet the new requirements will probably involve the use of shoulder belt type passenger seats in transport category aircrafts.
Only few energy absorption systems have been proposed which can affect the backrest of the seat and can therefore be used on such shoulder belt type passenger seats.
Thus, for instance, U.S. Pat. No. 6,209,955, involving a deformable back seat structure, U.S. Pat. No. 5,676,421 proposing multiple fragmentation pins on the back seat, U.S. Pat. No. 5,320,308 proposing a structural “breakover” device in association with a friction brake or clutch arrangement on the seat back, or EP 0 651 957 proposing a back seat structure with damping structural parts.
DE 19648974 proposes a rather complex energy absorption device, involving torsion bars and breakable connecting pieces, to be used on the underframe seat structure as well as at different levels of the back seat structure.
U.S. Pat. No. 4,688,662 on the other hand describes an energy absorber system on the interconnection of the seat bottom frame and the seat back frame The system utilises a pair of housings having facing cavities and a hollow deformable torsion member interconnecting the housings.
These state of the art energy absorption systems show several drawbacks with respect to the new criteria referred to above.
It is the object of the present invention to provide an absorption device which meets the following objectives:    1. To restrain the passenger's body in the required dynamic conditions by means of a shoulder harness, single or double, featuring one or two attachments at the top of the frame of the backrest, in association with a lap belt, as currently used in automotive or other applications (such as aircraft applications),            comprising rotation means allowing the backrest to break over when loaded forward by the shoulder belts, when the said loads exert a momentum exceeding a predetermined static resistance momentum on a specific part of the device. This component is working directly against the pivot axis of the backrest and is allowed a rotational, energy absorbing stroke, with the same angular amplitude than the backrest breakover, under constant application of the predetermined momentum;        to extend this protection to scenarios of successive impacts including the full range of loading less than, and up to, the ultimate required in a variety of directions, while keeping the energy absorption capacity to smooth off the peak of the impact pulses at the predetermined and built-in value.        
To allow the return (or rebound) of the occupant to his initial raised up position after each impact breakover.    2. To perform all functions in normal use by the passengers and crew, in particular the control of the backrest recline as provided for in conventional seats.            The backrest recline control device is characterised by its integration with the breakover control system, working on the same backrest axle, sharing the space available with the energy absorption system in the breakover mode. Functionally the two systems are independent and provisions are made to avoid any interference in the range of designed angular motions of the backrest, either in recline or in breakover.            3. To provide for easy selection of recline and break-over angular limitations, as required by the cabin layout, and current regulations. Specific means to select the range of angular motions are provided, for use by the maintenance crew.    4. To make use of conventional technology in the design & manufacturing.    5. To design for the lowest possible weight and production cost    6. To design for a minimum maintenance cost    7. To be compatible with a conventional seat configuration & its installation in a current, pressurised, transport category aircraft